This story is part of a regular history series in a weekly newspaper targeted at religious Jews. If this appeared in the NY Times or on Sixty Minutes, I'd be suspicious too.
Regenstein also publishes on lewrockwell.com. You can find a slightly different version of this article there as well as a letter on Grant that Regenstein sent to the New York Times there: "Rumsfeld Admires War Criminal."
Regenstein is definitely preoccupied with Grant and with his own Moses ancestors. How far he goes along with Rockwell's own obsessions, I don't know.
As South Africa and Rhodesia did for some time, the Old South welcomed Whites of different ethnic backgrounds who had useful talents and could fill important economic niches. Gentry and frontier societies have often shown such openness.
It's admirable, but ought to be seen in context. There were specific reasons and limits to that toleration.